JPS61187282A - Photodetecting element - Google Patents

Abstract

PURPOSE:To read a chrominance signal having high resolving power by mounting three kinds of photodiodes, which detect short wavelength beams, medium wavelength beams and long wavelength beams projected, consist of pnpnp structure and obtain several photocurrent, and a switch controlling these photodiodes. CONSTITUTION:Among beams projected to a light-receiving surface in a photodetecting element, short wavelength beams hu11 are absorbed to a p-n junction between a p-type layer 16 as a first layer and an n-type layer 17 as a second layer, and function as photocurrents I11 in a photodiode PD11, medium wavelength beams hu12 are absorbed to an n-p junction between the n-type layer 17 as the second layer and a p-type layer 18 as a third layer, and serves as photocurrents I12 in a photodiode PD12, and long wavelength beams hu13 are absorbed to a p-n junction between the p-type layer 18 as the third layer and an n-type layer 19 as a fourth layer, and function as photocurrents I13 in a photodiode PD13. When bias voltage V1-V4 is applied previously and MOS switches S11-S13 are brought simultaneously to ON stages, potential differences are generated in electrodes d-f, and chrominance signals corresponding to wavelengths can be read. Accordingly, color discrimination can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a photodetecting element that utilizes the photovoltaic effect to perform color sensing without using a color filter.

[Conventional technology]

An example of a conventional photodetection element is shown and explained in FIG. 3. FIG. 3 is a sectional view showing a conventional photodetection element that does not use a color filter.

In the figure, 1 is a protective film (8i0s), 4 is a p-type silicon substrate, and 3 is an n-type silicon substrate formed on this p-type silicon substrate 4.
A type layer 2 is a p-type layer formed within this n-type layer 3.

Note that hold and hu2 respectively indicate short wavelength light and long wavelength light incident from the outside, a and b indicate the respective electrodes of the n-type layer 2 and n-type layer 3, and C indicates the electrode of the p-type silicon substrate 4. .

The operation of the photodetecting element constructed in this way will be explained with reference to FIG. 4, which is a circuit similar to that shown in FIG.

First, short-wavelength light incident from the outside is exposed to the upper n-type layer 2.
is absorbed by the pn junction of the n-type layer 3, resulting in a photocurrent 11 of the photodiode PDI shown in FIG.

Next, the long wavelength light hu2 incident from the outside is absorbed by the lower n-type layer 3 and the np layer of the p-type silicon substrate 4, and becomes a photocurrent Is of the photodiode PDlI shown in FIG. Each photocurrent Ii, Is is obtained by the diodes PDl, PDg, and these photocurrents II,
Color discrimination can be performed depending on the value of the ratio I 2 /I 1 of Is, which corresponds to the incident light.

[Problem that the invention seeks to solve]

Conventional photodetecting elements such as those described above have problems such as a marked decrease in resolution for color discrimination and a limit to color separation.

This invention was made to solve these problems, and it provides a photodetector element that can significantly improve color discrimination and realize color reproducibility close to natural colors with a simple configuration. The purpose is to obtain.

[Failure to solve the problem]

The photodetecting element according to the present invention has a pnpnp structure and has three types of photodiodes that detect incident short wavelength light, medium wavelength light, and long wavelength light to obtain each photocurrent, and a control function for controlling these three types of photodiodes. The device is equipped with a switch to

[Effect]

In this invention, three types of photodiodes are used to obtain photocurrents corresponding to short wavelength light, medium wavelength light, and long wavelength light, respectively, and by applying a bias in advance, MO
A B-type switching potential difference is generated, making it possible to read color signals with higher resolution.

〔Example〕

Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 is a sectional view showing an embodiment of a photodetecting element according to the present invention.

In the figure, 11 is the drain electrode of the first layer to which the bias voltage Vl is applied, 12 is the drain electrode of the second layer to which the bias voltage Vg is applied, and 13 is the drain electrode of the third layer to which the bias voltage ■8 is applied. , 14-1.14-2.
14-3 is a MOS type switch, 15 is a gate electrode that simultaneously turns on each of these MOS type switches 14-1 to 14-3, 16 is a first p-type layer, and 17 is a second n-type layer. , 18 is the third p-type layer, 19 is the fourth n-type layer
The type layer 20 is a p-type substrate.

Further, V4 indicates the bias voltage applied to the fourth n-type layer 19, and d, e, and f respectively indicate the bias voltage applied to the first p-type layer 19.
6. Second n-type layer 17. Each electrode of the third n-type layer 18 is shown.

FIG. 2 is an equivalent circuit diagram of FIG. 1. In this Fig. 2, the same reference numerals as in Fig. 1 indicate corresponding parts, and PDli
-PD18 is a photodiode, 811°812, 5
ill is a MOS switch, and each of these MOS switches S
ll, 812.81s are MOS in Fig. 1, respectively.
It corresponds to switches 14-1, 14-2, and 14-3.

Next, refer to Figure 2 for the operation of the embodiment shown in Figure 1.
I will refer to and explain.

First, among the light incident on the light receiving surface of the photodetector, short wavelength light hun is absorbed by the pn junction between the first p-type layer 16 and the second n-type layer 17, and the photodiode PDI shown in FIG.
The photocurrent of I becomes 11, and the medium wavelength light hu I& is absorbed by the np junction between the second n-type layer 11 and the third n-type layer 18, and the photocurrent of photodiode PD12 in FIG. 2 becomes 112.
Furthermore, the long wavelength light hu la is absorbed by the pn junction between the third n-type layer 18 and the fourth n-type layer 19, and the second
The photocurrent Its of the photodiode PD 18 in the figure is obtained.

As shown in FIG. 2, the bias voltage V1.
If V2, VB, and V4 are applied, when the MOS switches Sll and S12.5ill are turned on at the same time, a potential difference is generated between the electrodes d, e, and f, and a color signal corresponding to the wavelength can be read out. Furthermore, in order to reset the circuit, the gate electrodes 15 of the MOS switches 14-1 to 14-3 shown in FIG. 1 are controlled and the MOS switches 811. It is sufficient to turn SN2, 818 into the OFF state.

In this way, it is composed of three types of photodiodes PDII to PDIB with a pnpnp structure that detect the short wavelength light huu, medium wavelength light hu1g, and long wavelength light huia incident on the light receiving surface to obtain each photocurrent l1l-Its. Therefore, color discrimination can be significantly improved, and color reproducibility close to natural colors can be achieved without the slight influence of hue unlike color filters.

In addition, in the above embodiment, the case where the picture element acts as a photodetecting element was explained as an example, but the present invention is not limited to this, and by making it into a play structure, it can be used as a color image sensor. You can also.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, color discrimination can be significantly improved with a simple configuration composed of three types of photodiodes without using complicated means, and color discrimination can be significantly improved without using complicated means. As shown in the figure, it is possible to achieve color reproducibility close to natural colors without being subtly affected by the tint of the filter, so the practical effect is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of a photodetecting element according to the present invention, FIG. 2 is an equivalent circuit diagram of FIG. 1, FIG. 3 is a sectional view showing an example of a conventional photodetecting element, and FIG. is an equivalent circuit diagram of FIG. 3. 11~13・Fist・Drain electrode, 14-1~14-3
...MOS switch, 15...gate electrode, 1
6...First p-type layer, 17.Fist...Second n-type layer, 18...Third p-type layer, 19...Fourth n-type layer , 2011@@・p-type substrate.

Claims (2)

[Claims] (1) Equipped with three types of photodiodes that have a pnpnp structure and detect incident short-wavelength light, medium-wavelength light, and long-wavelength light to obtain each photocurrent, and a switch that controls these three types of photodiodes. A photodetecting element characterized by: (2) The photodetecting element according to claim 1, wherein the switch for controlling the three types of photodiodes is constituted by a switch having a MOS type structure.